I'm playing around with the idea of converting my normal 2-car garage into a tandem garage - just in case I need the extra stall in the future.

I'm trying to minimize the depth of the garage and I have plenty of room for stuff along the walls and in the 4th bay, but it still looks like the garage needs to be at least 36' deep. And, of course, that doesn't allow room for an engine lift or other stuff in front of the car.

Arlie, I've looked at houses with tandem garages, and the thing that always strikes me is that you would have to play musical cars to get to the one in the back. Since you'd be building 3 walls anyway, and pouring a new foundation and floor for the addition, can I suggest just building a small shop in your backyard. I can't remember how much room you have on the south side of your house to access it, but if there's enough, it would simplify your life. Another option is a storage unit. They used to be about $65 a month for a car sized one, at least over here. You could store a car for 10 years and still be cheaper that adding on to the front of your garage.